When a multilevel VSB (Vestigial SideBand) modulated signal is demodulated, it is necessary to correct (hereinafter, ‘equalize’) the phase and amplitude of the received signal to compensate for channel distortion and fading. Particularly when the channel distortion is large or the channel characteristics change greatly over time, techniques for improving equalization accuracy and for assured tracking of rapid channel changes are needed.
In the general category of equalization there are time domain equalization and frequency domain equalization. Time domain equalization is an equalization method that feeds the received signal into an adaptive filter and corrects distortion in the received signal while optimizing the filter coefficients by use of an adaptive algorithm. Frequency domain equalization is an equalization method that detects the time domain CIR (Channel Impulse Response) on the basis of the received signal, executes a Fourier transform on the detected response, and equalizes the waveform in the frequency domain. In the ATSC (Advanced Television Systems Committee) broadcast standard, which uses VSB modulation and has been adopted in North America, for example, a field synchronization signal is inserted in the standard data frame as a known PN code signal; a known method of frequency domain equalization uses this signal as a reference signal in performing CIR detection (see, for example, Patent Reference 1).